Patent Application
20240426759
The present disclosure relates to the chemical analysis of liquid metals and alloys. More particularly, the present disclosure relates to use of laser-induced breakdown spectroscopy for the chemical composition analysis of liquid metals and alloys.
In metal production, monitoring the chemical composition of the produced metal is of critical importance. For example, in primary production of aluminum using continuous electrolysis according to the Hall-Héroult process, samples of metal from individual reduction cells are collected regularly for chemical analysis. This is done to monitor the level of impurities in the metal, which also serves as an indicator of the working condition of each cell.
A typical primary aluminum smelter will contain hundreds of reduction cells, from which samples are routinely collected (up to daily) during normal operation. The current standard practice involves extracting samples of liquid metal from the reduction cells and casting solid samples using standard sample molds, e.g. according to ASTM standard E716. The solid samples are subsequently analyzed for determining their chemical composition.
For decades, the standard method of analysis of solid samples in the aluminum industry has been spark atomic emission spectroscopy (also known as spark optical emission spectroscopy or spark-OES), e.g. according to ASTM standard E1251. Before performing spark-OES analysis, samples need to be suitably prepared, e.g., by mechanically milling to a certain depth into the cast sample. All the steps of sample preparation are important to ensure accurate analysis results.
LIBS measurement systems are disclosed that are configured to monitor the temperature of a molten metal sample during cooling of the molten metal sample in a crucible, and to initiate a LIBS measurement after the temperature of the molten metal sample satisfies measurement temperature criteria. The system may also monitor the temperature of an empty crucible to assist in ensuring that the crucible temperature is (i) sufficiently high to ensure that after the molten metal sample is delivered to the crucible and cools to satisfy the measurement temperature criteria, a sufficiently low cooling rate of the molten metal sample occurs during the LIBS measurement, and (ii) optionally sufficiently low to avoid an unnecessarily long cooling time of the molten metal sample prior to satisfying the measurement temperature criteria and initiation of the LIBS measurement. The LIBS measurement system may be mobile and battery-powered, and may include an integrated calibration station.
Accordingly, in one aspect, there is provided a method of performing laser-induced breakdown spectroscopy (LIBS) on a molten sample during cooling of the molten sample, the method comprising:
The method may further comprise, prior to introduction of the molten sample:
In some example implementations of the method, the crucible temperature criteria comprises a minimum crucible temperature, such that the crucible temperature criteria is satisfied when the minimum crucible temperature is exceeded. The minimum crucible temperature may reside between 100° C. and 60% of the melting point temperature of the molten sample in degrees Celsius. The minimum crucible temperature may reside between 15% of the melting point temperature of the molten sample and 60% of the melting point temperature in degrees Celsius.
In some example implementations of the method, the crucible temperature criteria is satisfied when the temperature of the crucible resides within a crucible temperature range. A maximum crucible temperature of the crucible temperature range may be defined such that when the temperature of the crucible equals the maximum crucible temperature and the molten sample is added to the crucible, the temperature of the molten sample satisfies the measurement temperature criteria within 1 minute. A maximum crucible temperature of the crucible temperature range may be defined such that when the temperature of the crucible equals the maximum crucible temperature and the molten sample is added to the crucible, the temperature of the molten sample satisfies the measurement temperature criteria within 30 seconds. The maximum crucible temperature may reside between 50% of the melting point temperature of the molten sample in degrees Celsius and 90% of the melting point temperature.
In some example implementations of the method, the measurement temperature criteria is selected such that the LIBS measurement is performed within a pre-selected measurement temperature range.
In some example implementations of the method, the measurement temperature criteria comprises a pre-selected measurement temperature, and the LIBS measurement is initiated immediately after (i) determining that the temperature of the molten sample equals the pre-selected measurement temperature and (ii) positioning a LIBS measurement head over the crucible.
In some example implementations of the method, the measurement temperature criteria comprises a pre-selected measurement temperature, and the LIBS measurement is performed after determining that the temperature of the molten sample equals the pre-selected measurement temperature. The pre-selected measurement temperature may exceed the melting point temperature of the molten sample by an amount ranging from 5% to 25% of the melting point temperature in degrees Celsius.
In some example implementations of the method, the measurement temperature criteria comprises a pre-selected measurement temperature range, and the LIBS measurement is performed while the temperature of the molten sample resides within the pre-selected measurement temperature range.
In some example implementations of the method, the measurement temperature criteria is configured such that the temperature of the molten sample during the LIBS measurement exceeds the temperature of the crucible when the crucible temperature criteria is satisfied.
In some example implementations of the method, the crucible is preheated by a previously measured molten sample, wherein the previously measured molten sample is discarded prior to measuring the temperature of the crucible.
In some example implementations of the method, the molten sample comprises aluminum and the crucible is preheated by contact with a cryolite crust formed on the top of a reduction cell.
In some example implementations of the method, the temperature of the crucible and the temperature of the molten sample are measured using a common temperature sensor.
In some example implementations of the method, the temperature of the crucible and the temperature of the molten sample are measured in absence of contact.
In some example implementations of the method, the crucible is supported by a crucible support during LIBS measurement. LIBS measurements may be performed by a LIBS subsystem, and wherein a measurement head of the LIBS subsystem is movable from a parked position to an operative position in which the measurement head resides above the crucible support, and a heat shield is positioned to thermally shield the measurement head from heat radiating from the crucible when the measurement head resides in the parked position.
In some example implementations of the method, the crucible is a metallic crucible. The crucible may be formed from structural steel.
In some example implementations of the method, a heat capacity of the crucible resides between 400 and 500 J/K.
In some example implementations of the method, a thermal conductivity of the crucible resides between 40 and 50 W/m-K.
In some example implementations of the method, the crucible is a first crucible, the molten sample is a first molten sample, the method further comprising:
The first crucible may be supported by a primary crucible support during the LIBS measurement performed on the first molten sample; and wherein, after replacing the first crucible with the second crucible, the first crucible is placed on a secondary crucible support for cooling.
In some example implementations, the method further comprises, prior to replacing the first crucible with the second crucible:
In some example implementations, the method further comprises:
In some example implementations of the method, the LIBS measurement is performed by a LIBS system residing on a portable support structure, and the LIBS system is powered by a battery.
In another aspect, there is provided a method of performing laser-induced breakdown spectroscopy (LIBS) on a molten sample during cooling of the molten sample, the method comprising:
In some example implementations, the method further comprises, after preheating the crucible and prior to introduction of the molten sample into the crucible:
In another aspect, there is provided a system for performing laser-induced breakdown spectroscopy (LIBS), the system comprising:
The processing circuitry may be further configured to perform the following operations prior to introduction of the molten sample into the crucible:
In another aspect, there is provided a portable system for performing laser-induced breakdown spectroscopy (LIBS), the portable system comprising:
In some example implementations, the system further comprises:
In some example implementations, the system further comprises the crucible and the additional crucible, wherein the crucible and the additional crucible are metallic. The crucible and the additional crucible may be formed from structural steel.
In some example implementations, the system further comprises the crucible and the additional crucible, wherein heat capacities of the crucible and the additional crucible reside between 400 and 500 J/K.
In some example implementations, the system further comprises the crucible and the additional crucible, wherein thermal conductivities of the crucible and the additional crucible reside between 40 and 50 W/m-K.
In another aspect, there is provided a portable system for performing laser-induced breakdown spectroscopy (LIBS), the portable system comprising:
In some example implementations of the system, the integrated calibration apparatus comprises a LIBS calibration reference material suitable for calibrating a signal of the LIBS subsystem when the measurement head resides in the calibration position. The integrated calibration apparatus may comprise a support frame, and wherein the LIBS calibration reference material is movable relative to the support frame such that when the measurement head is repositioned in the calibration position to perform a subsequent calibration measurement, a different region of the LIBS calibration reference material can be optically interrogated by the measurement head, thereby facilitating reuse of the LIBS calibration reference material during multiple calibration measurements.
In some example implementations of the system, the measurement head comprises a distance sensor, and wherein the integrated calibration apparatus is an integrated distance sensor calibration apparatus, the integrated distance sensor calibration apparatus comprising a contact location and a target location, the contact location being located on the integrated calibration apparatus such that when the measurement head resides at the calibration position and is contacted with the contact location after lowering the measurement head along a direction parallel to an optical axis of the measurement head, a known spatial offset resides between the distance sensor and the target location, thereby facilitating calibration of the distance sensor. The integrated distance sensor calibration apparatus may be elastically biased such that the known spatial offset is maintained when the measurement head is moved along the direction after having made contact with the contact location.
In some example implementations, the system further comprises:
A further understanding of the functional and advantageous aspects of the disclosure can be realized by reference to the following detailed description and drawings.
Embodiments will now be described, by way of example only, with reference to the drawings, in which:
Various embodiments and aspects of the disclosure will be described with reference to details discussed below. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure.
As used herein, the terms “comprises” and “comprising” are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in the specification and claims, the terms “comprises” and “comprising” and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components.
As used herein, the term “exemplary” means “serving as an example, instance, or illustration,” and should not be construed as preferred or advantageous over other configurations disclosed herein.
As used herein, the terms “about” and “approximately” are meant to cover variations that may exist in the upper and lower limits of the ranges of values, such as variations in properties, parameters, and dimensions. Unless otherwise specified, the terms “about” and “approximately” mean plus or minus 25 percent or less.
As used herein, percentage values associated with temperatures are intended to refer to temperatures in degrees Celsius.
It is to be understood that unless otherwise specified, any specified range or group is as a shorthand way of referring to each and every member of a range or group individually, as well as each and every possible sub-range or sub-group encompassed therein and similarly with respect to any sub-ranges or sub-groups therein. Unless otherwise specified, the present disclosure relates to and explicitly incorporates each and every specific member and combination of sub-ranges or sub-groups.
As noted above, the conventional approach to chemical analysis in the aluminum industry employs the use of spark-OES on solid samples. Unfortunately, this conventional approach involves a number of technical problems that can impede the ability to achieve accurate chemical analyses.
In particular, the sample preparation process can lead to the introduction of errors. For example, errors may be introduced during the sample preparation process due to numerous potential causes, including, but not limited to, (i) temperature variations of the melt or mold when sampling is carried out, (ii) uneven pouring into sample molds, (iii) segregation related to the cooling rate of the metal, (iv) porosity, cracks or voids in the sample, (v) excessive surface roughness or smoothness after milling, and (vi) contamination of the surface before analysis.
Moreover, the conventional approach to casting samples and performing subsequent analysis can lead to the possibility of errors arising due to confusion between individual samples. Yet another problem associated with the conventional chemical analysis workflow is the safety hazard that can be caused by traffic inside the smelter that results from the transport of cast samples to a laboratory. Considering the steps of collecting liquid metal, casting solid samples, transporting samples to a central analysis facility, performing mechanical preparation and chemical analysis, hours may pass from the time that metal is sampled until analysis results are available to plant operators to make process decisions.
The present inventors, having identified and carefully considered the aforementioned technical and workflow challenges, set out to develop a new approach to chemical analysis that would overcome the problems associated with the conventional approach to chemical analysis. In particular, the present inventors recognized that in order to overcome these technical problems, a new chemical analysis modality would be needed that facilitates robust, rapid and accurate chemical testing in a real-time and in situ manner.
Various attempts have been made to adapt different detection modalities for real-time monitoring of the status of reduction cells in primary aluminum smelters. Some of these approaches include analysis of cell temperature and bath chemistry, analysis of individual anode current signals, analysis of cell voltage noise, and optionally a multiple of additional parameters affecting the current efficiency, energy consumption and operational lifetime of the cell. Differential thermal analysis has been successfully applied to determine bath chemistry, i.e., bath ratio and alumina (Al2O3) content, within a few minutes using, e.g., the commercially available STARprobe™ replacing the alternative time-consuming sample preparation and X-ray analysis in a central laboratory (X. Wang: “Alcoa STARprobe™—Update in Further development for measuring cryolite properties,” TMS Light Metals 2016, pp. 397-402).
The real-time and in situ measurement of chemical impurities in the produced metal, however, presents a distinct challenge that is not addressed by the aforementioned real-time monitoring methods. Laser-induced breakdown spectroscopy (LIBS), an atomic emission spectroscopy technique applicable to the measurement of liquids and solids, has emerged as a promising technology for the chemical analysis of liquid metal. In particular, LIBS has previously been applied to measure the impurity content of liquid aluminum (A. K. Rai, F. -Y. Yueh, J. P. Singh: “Laser-induced breakdown spectroscopy of molten aluminum alloy,” Appl. Opt. 42 (2003) pp. 2078-2084; J. Herbert, et al.: “The Industrial Application of Molten Metal Analysis,” TMS Light Metals 2019, pp. 945-952; S. H. Gudmundsson, et al.: “Accurate Real-Time Elemental (LIBS) Analysis of Molten Aluminum and Aluminum Alloys,” TMS Light Metals 2020, pp. 860-864.)
Attempts to adapt LIBS to real-time and in situ testing in industrial environments have been fraught with difficulties. For example, the complex and hazardous environment inside a primary aluminum smelter presents many technical challenges for the use of a LIBS system due to high temperatures, dust, and fumes emitted from the cells when opened. In addition, high magnetic fields present in the proximity of the reduction cells a challenge to operating measurement equipment (see, e.g., Sun et al., Spectrochimica Acta Part B 142 (2018) 29-36). While compact hand-held LIBS analyzers are available from several vendors, they are not suitable for analyzing liquid metal and do not provide the detection limits or accuracy required for monitoring aluminum from reduction cells.
Accordingly, despite the promise of LIBS for improved chemical composition analysis, there remains a need to solve outstanding technical challenges in order to facilitate the adaptation of LIBS to a real-time and in situ implementation that is sufficiently robust to deliver rapid and accurate chemical analysis of molten metals.
One problem encountered by the present inventors when attempting to adapt a LIBS measurement system in a portable configuration was the need to ensure a consistent measurement temperature of the molten metal sample during a LIBS measurement. Specifically, the relative intensities of LIBS emission lines can be dependent on sample temperature, with the consequence that variations in sample temperature among successive LIBS measurements can lead to significant errors in reported concentrations of impurities.
Although such a problem can potentially be addressed by actively controlling the temperature of the molten metal sample prior to or during LIBS measurement, such an approach can be problematic for a portable implementation due to the high power consumption of active heat sources, which can preclude the ability to power a portable system using batteries.
The present inventors sought to overcome these technical problems by developing a LIBS system that employs passive cooling of the molten metal sample, thus avoiding the need for active heating prior to, or during, the LIBS measurement. Moreover, it was determined that such an implementation could be adapted to facilitate accurate and repeatable LIBS measurements of subsequently measured samples without introducing significant measurement errors from variations in sample temperature, by monitoring the temperature of a molten metal sample during cooling of the molten metal sample and initiating a LIBS measurement when or after the monitored temperature satisfies pre-selected measurement temperature criteria. Such an implementation can be particularly beneficial in a mobile configuration due to the absence of a need for active heating of the molten metal sample prior to, and during, the LIBS measurement process, which can greatly simplify the system design and facilitate a battery-powered configuration. Furthermore, the implementation avoids having to introduce additional complications to the spectral analysis to detect and correct for the effects of temperature variation of the melt.
The monitoring of the temperature of the molten metal sample and initiation of the LIBS measurement only when measurement temperature criteria is satisfied ensures that LIBS measurements made on different molten metal samples (e.g. different samples from a common cell or different samples from different cells), which may have different initial temperatures, or different cooling rates due to different temperatures of the measurement crucible, are nonetheless performed at or near a common temperature during LIBS measurement. Such an example implementation thereby avoids, prevents or reduces measurement errors due to changes in sample temperature.
As will be described below, the present example embodiments can be beneficial in reducing the sources of error in analysis by analyzing the metal in the liquid state and by facilitating the immediate, direct, and unambiguous correlation of the chemical analysis results to a respective reduction cell. The present example systems and methods further facilitate a consistent and rapid workflow when measuring samples from multiple pots in sequence. Similarly, the present example systems and methods may be employed to facilitate rapid measurements of a series of samples extracted from a single reduction cell, or any similar manner in which multiple samples of liquid metal from a single source or a plurality of sources need to be analyzed in a rapid an accurate fashion.
Accordingly, in some example implementations, a portable chemical analysis system includes a LIBS measurement subsystem and a temperature sensor configured to monitor the temperature of a molten metal sample during passive cooling of the molten metal sample. The portable measurement system compares the measured temperature of the molten metal sample and controls the LIBS measurement subsystem to initiate the LIBS measurement after pre-selected measurement temperature criteria is satisfied.
An example embodiment of such a portable LIBS system is shown in
The molten metal sample 10 is passively cooled within a crucible 20 (e.g. ladle) prior to performing LIBS measurement while monitoring the temperature of the metal molten sample 10, as illustrated, for example, in
Referring again to
The measurement temperature criteria ensures that LIBS measurements made on different molten metal samples (e.g. different samples from a common cell or different samples from different cells) are performed at or near the same temperature, thereby avoiding, preventing or reducing measurement errors due to changes in sample temperature, as discussed above. For example, the LIBS measurement head 200 may be controlled such that the LIBS measurement is initiated (i) immediately after the measurement temperature criteria is satisfied, (ii) after a fixed delay after the measurement temperature criteria is satisfied, or (iii) within a prescribed time interval after the measurement temperature criteria is satisfied, where said time interval may be calculated based on the observed cooling rate.
In one example implementation, the measurement temperature criteria may be satisfied when the measured temperature of the molten metal sample 10 reaches a measurement temperature, such as, for example, a measurement temperature exceeding the melting point temperature of the molten sample by 5%, or for example by 10%, or for example by 15%, or for example by 20%, or for example by 25%. In the example case of molten aluminum, a measurement temperature selected from the range of 700-800° C., such as 750° C.
In cases in which the LIBS measurement head 200 resides in a parked position (e.g. as shown at 201 in
Prior to performing LIBS analysis, the surface of the molten metal sample may be skimmed with an automated skimmer (not shown in
It was found by the present inventors that the rate of cooling of the molten metal sample 10 during the LIBS measurement can impact the accuracy of the LIBS measurements. In particular, if the cooling rate is sufficiently high, the resulting temperature variation during the LIBS measurement step (which can involve a duration of several seconds, such as, for example, approximately 5 seconds) can lead to inaccuracies in the determination of impurity concentrations. Furthermore, a large variation in temperature during the LIBS measurement step can render the system susceptible to measurement errors if the timing of the LIBS measurement, relative to the time of determination of the measurement temperature criteria being satisfied, is not accurately controlled. Similarly, a high cooling rate can negatively impact the consistency of the measurement conditions of a series of measurements of different liquid metal samples.
This problem can be exacerbated when the crucible is made from a material that can lead to rapid cooling of the molten metal sample. For example, in order to facilitate rapid removal of the molten metal sample after LIBS measurement, it may be useful or necessary to contact the crucible with an impact surface to dislodge solidified metal from the crucible. In such cases, it may be beneficial to use a non-ceramic crucible that is capable of withstanding the impact without risk of breakage. One example of a suitable crucible is a metallic crucible, such as a crucible fashioned from structural steel. Given that such metallic crucibles typically have a high heat capacity and high thermal conductivity, it follows that a molten metal sample can rapidly cool within a cold metal crucible. In some example implementations, the heat capacity of such crucibles may reside between 400 and 500 J/K and the thermal conductivity of the crucible material may reside between 40 and 50 W/m-K.
In order to avoid or reduce errors induced by rapid cooling of the molten metal sample, the present inventors found that it can be beneficial to pre-heat the crucible 20 prior to delivery of the molten metal sample 10 to the crucible 20. Such pre-heating can be beneficial in reducing and/or controlling the rate of cooling of the molten metal sample 10 after the molten metal sample is received by the crucible 20. In addition, pre-heating improves the safety of the liquid metal sampling process by ensuring that crucibles are free of moisture before the introduction of liquid metal.
The preheating of the crucible can be performed according to a variety of methods. In some example embodiments, the preheating is performed external to the portable LIBS measurement system, such as by utilizing available heat from the reduction cells. For example, in an example implementation involving an aluminum smelter, the crucible may be preheated by placing it in contact with a cryolite crust formed inside the reduction cell for a sufficiently long period of time for the crucible to reach the desired temperature.
After pre-heating the crucible, the molten metal sample can be delivered to the crucible (e.g. measurement ladle). For example, a sample of liquid molten metal can be extracted using methods conventionally used for sampling metal from reduction cells, such as using a sampling ladle to collect molten metal from a reduction cell. For example, the sample of molten metal can be introduced manually to the sample crucible, e.g. by means of a human operator using such a sampling ladle. In addition, samples may be extracted, manually or automatically, from other types of sources such as a mixing furnace, holding furnace, or the like, where the sampling ladle can, in some embodiments, also be used as the sample crucible holding the sample during measurement.
In some example embodiments, it may be beneficial to ensure that the crucible 20 has been preheated by a sufficient amount to ensure that the cooling rate will not be inordinately rapid during the LIBS measurement. For example, prior to introducing the molten metal sample 10 into the crucible 20, the temperature of the crucible 20 may be measured and compared to crucible temperature criteria in order to evaluate whether or not the crucible 20 has been sufficiently pre-heated prior to receiving the molten metal sample 10. The measurement temperature criteria may be configured such that the temperature of the molten sample during the LIBS measurement exceeds the temperature of the crucible when the crucible temperature criteria is satisfied.
In some example implementations, the temperature sensor 210 that is employed to monitor the temperature of the molten metal sample 10 may be employed to measure the temperature of the empty crucible 20. Such an example implementation is illustrated in
In some example embodiments, the crucible temperature criteria may be defined such that it is satisfied when the measured crucible temperature exceeds a pre-selected minimum temperature value, such as, for example, a minimum temperature that lies within the range of 100° C. to 60% of the melting point temperature of the molten metal, or for example, 15-60% of the melting point temperature (e.g. 100-400° C. in the case of aluminum), thereby ensuring that the cooling rate of the molten metal sample 10 after the molten metal sample 10 is delivered to the crucible 20 is kept within certain limits. For example, the crucible temperature criteria can be selected such that the molten metal sample cools by fewer than 50° C. during the LIBS measurement, or for example, cools by fewer than 20° C. during the LIBS measurement, or for example, cools by fewer than 10° C. during the LIBS measurement, or for example, cools by fewer than 5° C. during the LIBS measurement.
In the absence of an upper limit on the permissible initial temperature of the crucible 20, the crucible 20 may in some cases be preheated to a temperature that, while satisfying the crucible temperature criteria, is so high that an excessive amount of time will elapse before the molten metal sample 10 cools to a temperature that satisfies the measurement temperature criteria. In such cases, the time required for collecting and analyzing subsequent samples will be correspondingly increased. Such cases may be avoided by defining the crucible temperature criteria such that the crucible temperature criteria is not satisfied by a crucible temperature that exceeds an upper temperature value. For example, the crucible temperature criteria may include a maximum crucible temperature that is selected to lie within the range of 50-90% of the melting point temperature (e.g. between approximately 330 and 600° C. in the example case of aluminum). A maximum crucible temperature limit additionally ensures that the degree of contamination of crucible material into the molten metal is minimized.
For example, the crucible temperature criteria may be satisfied when the temperature of the crucible 20 (prior to receiving the molten metal sample 10) lies with a pre-defined temperature range, such as, for example, a range of 100° C. to 60% of the melting point temperature of the molten sample, or, for example, 15-60% of the melting point temperature (100-400° C. in the example case of aluminum) or a range of 30-75% of the melting point temperature (e.g. 200-500° C. in the example case of aluminum). The pre-defined temperature range may thus characterize a “Goldilocks” range, such that that when a molten metal sample 10 is delivered to a crucible satisfying the crucible temperature criteria, the molten metal cools at a rate that is sufficiently slow to permit accurate LIBS measurement (when the temperature of the molten metal sample satisfies the measurement temperature criteria) and such that the molten metal sample cools to a temperature that satisfies the measurement temperature criteria within a sufficiently short time duration. For example, the maximum temperature permitted by the crucible measurement criteria may be defined such that the molten metal sample, after having been delivered to the crucible, cools to a temperature that satisfies the measurement temperature criteria within 1 minute, or within 30 seconds, or within 15 seconds.
In some example implementations, an indication may be provided to an operator when the temperature of the empty crucible 20 satisfies the crucible temperature criteria. Non-limiting examples of suitable indications include a displayed message, symbol or colour, and an audible alarm or message. The indication may be employed to prompt an operator that the empty crucible 20 is ready to receive the molten metal sample. In other example implementations, the temperature of the empty crucible 20 may be displayed. In such cases, an operator having knowledge of suitable crucible temperature criteria (e.g. a minimum crucible or a desired crucible temperature range) may deliver the metal molten sample to the crucible when the displayed temperature satisfies the known crucible temperature criteria.
Referring now to
If the crucible temperature criteria is satisfied, an indication can be provided that the crucible is ready to receive the molten metal sample, as shown at 320. After the molten metal sample is received in the crucible, the temperature of the molten metal sample is monitored, as shown at 330, during cooling, and the measurement temperature criteria is evaluated as shown at 340. When the measurement temperature criteria is satisfied, the LIBS measurement is initiated, as shown at 350.
In the example method described above with reference to
The problem associated with the delay in passive cooling an overheated crucible may be overcome by replacing the overheated crucible with a different crucible that has been preheated to a lower temperature. This process is schematically illustrated in
The first (overheated) crucible, after having been replaced by the second crucible, may be supported on a crucible holder integrated with the LIBS measurement system (e.g. integrated with a common mobile support). As illustrated in
As shown at step 420 in
During use of the second crucible, the first crucible is supported by the additional crucible support 32 and passively cools from its initially overheated state. The temperature of the first crucible may be intermittently measured in order to determine when the first crucible again satisfies the crucible temperature criteria, as illustrated in
Referring again to
Step 450 illustrates an example scenario in which the second crucible is exchanged with a third crucible that has been preheated. Alternatively, as shown in step 460, the second crucible may be exchanged with the first crucible, since the first crucible will have cooled during the use of the second crucible for LIBS measurements. These options are schematically illustrated in
While the preceding example implementations employ one or two additional crucible supports, three or more crucible supports may be included in order to provide additional locations for the cooling of crucibles. The number of crucible supports needed may depend on the rate of analysis and the need to ensure a continuous operation when measuring from multiple sampling points.
As explained above, in some example implementations, the LIBS measurement head 200 may reside in a parked position prior to performing LIBS analysis. For example, the LIBS measurement head may be translated (e.g. robotically translated) laterally and/or vertically to a parked position during monitoring of the molten metal sample in order to provide a sufficient line of sight for non-contact temperature sensing. The LIBS measurement head may also be translated to a parked position to perform one or more calibration steps, as described in further detail below.
In some example embodiments, one or more calibration devices may be employed to calibrate the LIBS measurement head 200 when the LIBS measurement head 200 resides in a parked position.
For example, during some implementations of LIBS analysis, it can be beneficial to ensure a consistent distance between the liquid metal surface and the excitation and detection optics (e.g. the distal region of the LIBS measurement head 200). This distance can be controlled with any suitable type of distance sensor that provides feedback to the mechanical translation mechanism of the LIBS measurement head 200. However, during a measurement run, the LIBS measurement head can be subjected to significant variations in ambient temperature as well as heating due to thermal radiation from the sample and the measurement ladles, and this heating can be exacerbated in non-laboratory settings, such a pot room of an aluminum smelter. In order to ensure rapid and repeatable measurements, a calibration station may be incorporated into the system (e.g. supported with the LIBS system by a common mobile support structure) that allows a distance sensor to be calibrated prior to a given (optionally, each) measurement, thus correcting, at least in part, for thermal drift in the system.
An example implementation of a calibration station for calibrating a distance sensor is shown in
In some example embodiments, the calibration station may facilitate multiple calibrations, including, but not limited to, the calibration of a distance sensor and the use of one or more reference materials to calibrate the response of the LIBS measurement system. In some example implementations, one or more calibration steps may be autonomously performed when one or more conditions are met, such as, for example, after a selected number of samples have been measured, after a detected change in ambient conditions, and/or after an elapsed time.
Referring again to
Although many of the present example embodiments relate to a portable LIBS system, it is noted that in other example embodiments, the support that supports the LIBS measurement subsystem may be a fixed support. For example, any of the present example systems or methods may be adapted to a non-portable configuration, such as a system configuration suitable for implementation at a furnace, launder or other fixed source of liquid metal, either in a plant/smelter or a laboratory setting. In such settings, the sampling may be advantageously automated (e.g., by using a robot arm).
Furthermore, while many of the preceding example implementations employ the passive cooling of the molten metal sample prior to LIBS analysis, and/or the passive cooling of an overheated crucible prior to further use, it will be understood that some implementations may employ active heating and/or active cooling. For example, in some example implementations, forced air may be employed to cool an overheated empty crucible residing on a crucible support. Feedback from a temperature sensor measuring the temperature of the crucible may be employed to control the cooling device to bring the empty crucible to a temperature that satisfies the crucible temperature criteria. Active heating may also optionally be employed to pre-heat one or more crucibles. For example, in some example implementations, one or more crucible supports may include a heat source (e.g. an inductive or resistive heater or a gas burner). Feedback from the temperature sensor measuring the temperature of the crucible may be employed to control the heat source to bring the empty crucible to a temperature that satisfies the crucible temperature criteria. In some example implementations, the system may include both active heating and cooling devices to control the temperature of one or more crucibles.
In other example implementations, active heating (such as inductive heating) and or cooling (such as forced air cooling) may be employed, in combination with the monitored temperature of the molten metal sample with the crucible, to stabilize the temperature of the molten metal sample prior to, or during, LIBS measurements.
The embodiments of the present disclosure can be applied to a variety of metals and metal alloys such as but not limited to aluminum, steel, steel alloys, iron, iron alloys, copper, zinc, lead and other metals and metal alloys in their liquid state and can be useful in industrial settings and applications as mentioned above.
It will be understood that the present disclosure is not intended to be limited to analysis of any particular elements and can be used both to determine concentration of the main components in the metal or alloy sample, or trace components. Accordingly, in some embodiments the method and/or apparatus is for determining in the liquid metal or alloy sample the true bulk concentration of one or more elements selected from Aluminum, Silicon, Phosphorus, Sulphur, Chloride, Calcium, Magnesium, Sodium, Titanium, Vanadium, Chromium, Manganese, Iron, Cobalt, Nickel, Copper, Zinc, Zirconium, Strontium, Niobium, Molybdenum, Ruthenium, Rhodium, Palladium, Silver, Cadmium, Tin, Antimony, Wolfram, Rhenium, Iridium, Platinum, Gold, Mercury, Lead and Bismuth. The method is also suitable for quantifying very light impurity elements such as Hydrogen, Lithium, Beryllium, Boron and Carbon that are difficult to detect with certain other analysis methods. Furthermore, it will be understood that trace impurities may be introduced to the liquid metal from the sampling equipment itself, e.g. sampling ladles and measurement crucibles. The present disclosure applies equally to measurement and identification of such contaminants.
Referring again to
In some example embodiments, the spectral analysis is based on a LIBS method where one or more laser pulses in sequence are directed to the sample surface through excitation optics, and light emitted from the sample is received through receiving optics and transmitted to a detector for recording spectral information of the detected light. Optical detection methods and subsequent processing of detected emission are as such known to the person skilled in the art. From the spectral information one or more emission peaks are then analyzed and typically compared to calibration values in order to obtain quantitative determination of one or more elements.
The excitation optics and receiving optics of the LIBS measurement subsystem may be fully separate or partly comprising the same optical elements. In a preferred implementation, the excitation means and receiving optics may be accurately positioned at a pre-determined distance from the sample surface for each individual excitation event. The accuracy of this positioning over time during field operation is advantageously maintained using a distance calibration function as described above.
A pulsed excitation laser employed in various example embodiments may be generally of conventional type as is used in present day LIBS configurations. According to the invention, stable excitation conditions may be provided with the optical excitation configured such that a sufficiently large and reproducible volume of the liquid metal sample is ablated during excitation and such that the chemical composition of this ablated fraction of the sample is representative of the composition of the whole sample.
In some embodiments a stream of inert gas, such as argon, helium or nitrogen, is fed from a source, such as a pressurized canister mounted on the same portable support as the LIBS system, through one or more gas channels to the vicinity of the sampling point to maintain an inert atmosphere during the LIBS measurement.
In some example embodiments, the receiving optics of the LIBS measurement head may include more than one lens, with the lenses optionally arranged radially around the point of contact of the laser pulse and sample surface. Light collected by the one 10 or more receiving optics can be transferred via fiber optics or other optical transmission means to the same spectrometer or to different spectrometers (for example, each lens in a plurality if lenses can transfer light to its respective spectrometer). In some embodiments such plurality of spectrometers may be configured so that each spectrometer collects emission at a limited wavelength range, so that the plurality of spectrometers together covers the entire desired wavelength range. In some embodiments, spectroscopic detection may also comprise detection of selected wavelength bands using one or more suitable bandpass filters and optical sensors.
Referring again to
The preceding example methods may be autonomously implemented according to modules 155, 160 and 165 of the control and processing circuitry 100. For example, the measurement of the temperature of the empty crucible, the monitoring of the temperature of the molten metal sample, and the evaluation of the crucible temperature criteria and the measurement temperature criteria, may be performed according to executable instructions implemented by the temperature monitoring module 155. Robotic control of the LIBS measurement head (and optionally one or more components of the calibration station 500) may be controlled according to the robotic actuation module 160, and LIBS measurement acquisition and data processing may be performed according to the LIBS measurement module 165.
It is to be understood that the example system shown in
For example, the control and processing circuitry may include a local computing subsystem that includes a first set of components supported by the support 50, where the local computing subsystem is connectable, through a network, to one or more external computing devices. The network may include a local and/or external network, where one or more segments of the network may be wireless. For example, in some implementations, data locally obtained and optionally processed by local computing subsystem may be transmitted to one or more external computing devices, such as, for example, an external control system residing within or remote from a metal processing plant, or, for example, one or more mobile computing devices such as mobile phones, laptops and tablet computing devices. Examples of such data include raw data, analysis results and/or status of equipment (which may include, for example, environment variables, error messages, alerts, or other measures or indications). The communication between the local computing subsystem and the one or more external computing devices may be unidirectional (e.g. for autonomous uploading of data to the remote computing devices) or bidirectional. In some example implementations, the local computing subsystem may be configured to receive one or more portable computing device in a “docked” configuration for transmitting data through a wired or wireless connection.
Although only one of each component is illustrated in
Control and processing circuitry 100 may be implemented as one or more physical devices that are coupled to processor 110 through one of more communications channels or interfaces. For example, control and processing circuitry 100 can be implemented using application specific integrated circuits (ASICs). Alternatively, control and processing circuitry 100 can be implemented as a combination of circuitry and software, where the software is loaded into the processor from the memory or over a network connection.
Some aspects of the present disclosure can be embodied, at least in part, in software. That is, the techniques can be carried out in a computer system or other data processing system in response to its processor, such as a microprocessor, executing sequences of instructions contained in a memory, such as ROM, volatile RAM, non-volatile memory, cache, magnetic and optical disks, or a remote storage device. Further, the instructions can be downloaded into a computing device over a data network in a form of compiled and linked version. Alternatively, the logic to perform the processes as discussed above could be implemented in additional computer and/or machine readable media, such as discrete circuitry components as large-scale integrated circuits (LSI's), application-specific integrated circuits (ASIC's), or firmware such as electrically erasable programmable read-only memory (EEPROM's) and field-programmable gate arrays (FPGAs).
A computer readable medium can be used to store software and data which when executed by a data processing system causes the system to perform various methods. The executable software and data can be stored in various places including for example ROM, volatile RAM, non-volatile memory and/or cache. Portions of this software and/or data can be stored in any one of these storage devices. In general, a machine readable medium includes any mechanism that provides (i.e., stores and/or transmits) information in a form accessible by a machine (e.g., a computer, network device, personal digital assistant, manufacturing tool, any device with a set of one or more processors, etc.).
Examples of computer-readable media include but are not limited to recordable and non-recordable type media such as volatile and non-volatile memory devices, read only memory (ROM), random access memory (RAM), flash memory devices, floppy and other removable disks, magnetic disk storage media, optical storage media (e.g., compact discs (CDs), digital versatile disks (DVDs), etc.), among others. The instructions can be embodied in digital and analog communication links for electrical, optical, acoustical or other forms of propagated signals, such as carrier waves, infrared signals, digital signals, and the like. As used herein, the phrases “computer readable material” and “computer readable storage medium” refer to all computer-readable media, except for a transitory propagating signal per se.
The following examples are presented to enable those skilled in the art to understand and to practice embodiments of the present disclosure. They should not be considered as a limitation on the scope of the disclosure, but merely as being illustrative and representative thereof.
Prior to introduction of a molten aluminum sample into a measurement crucible, the measurement crucible preheated to a temperature satisfying the crucible temperature criteria. After introducing a given molten aluminum sample into the measurement crucible, the temperature of the molten aluminum sample was monitored using a non-contact thermometer while passive cooling the molten aluminum sample, without performing active heating or active cooling of the crucibles. The LIBS measurement was carried out upon fulfilment of measurement temperature criteria as described above.
As demonstrated in
Measurements were typically collected from up to 50 reduction cells in sequence, where the features of the present example portable LIBS system enabled an average cycle time of around 90 seconds per cell. This included the time for sampling aluminum from the cells, cooling of the aluminum to satisfy the measurement temperature criteria, carrying out the LIBS measurement, and transportation of the analyzer between cells using the electric vehicle.
The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202141000474 | Jan 2021 | IN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IS2022/050007 | 9/7/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63260992 | Sep 2021 | US |
